Правильно построить запрос, и убрать ненужные параметры

procedure TForm1.Button13Click(Sender: TObject);
begin
  with SMSF do
    begin
      Close;
      SQL.Text:='Select * from CLIENTS where (EMAIL like :mail) AND (D_ROZH = :d_rozh)';
      If CheckBox1.Checked then ParamByName('mail').AsString:='';
      If CheckBox6.Checked then ParamByName('d_rozh').AsDate:=Date1.Date;
      Open;
    end;
end;

SQL.Text:='Select * from CLIENTS where (EMAIL = isNull (:mail,EMAIL)) AND (D_ROZH =  isNull (:d_rozh, D_ROZH ))';

procedure TForm1.Button13Click(Sender: TObject);
var
  LWhere: string;
begin
  LWhere := '';
  If CheckBox1.Checked then LWhere := LWhere + ' (EMAIL like :mail)';
  If CheckBox6.Checked then begin
    if LWhere <> '' then
      LWhere := LWhere + ' AND ';
    LWhere := LWhere + ' (D_ROZH = :d_rozh)';
  end;
  if LWhere <> '' then
    LWhere := ' WHERE ' + LWhere;
  with SMSF do
    begin
      Close;
      SQL.Text:='Select * from CLIENTS' + LWhere;
      If CheckBox1.Checked then ParamByName('mail').AsString:='';
      If CheckBox6.Checked then ParamByName('d_rozh').AsDate:=Date1.Date;
      Open;
    end;
end;

with SMSF do
    begin
      Close;
      Clear;
      SQL.ADD:='Select * from CLIENTS';
      If CheckBox1.Checked then 
             begin
                 ParamByName('mail').AsString:='';
                 SQL.ADD:='where (EMAIL like :mail)';
//и так далее...
      Open;
    end;